THE RAW MATERIALS OF GLASS MANUFACTURE.
General considerations--Chemical purity, moisture, and
physical condition, constancy of quality--Sources
of silica, sand and sandstone--Felspar--Sources of
alkali: Soda ash (carbonate of soda), salt-cake (sulphate
of soda), pearl ash (carbonate of potash)--Alkali
nitrates--Natural minerals containing alkalies--Sources
of other bases: Lime, chalk, limestone, slaked lime--
Gypsum (sulphate of lime)--Barium compounds--Magnesia
and zinc--Lead oxide, red lead--Aluminium, manganese,
arsenic--Carbon--Coke, charcoal, anthracite coal _p._ 35